Rotating shaft disconnect systems, in the general sense, are not new. For years, different applications have demanded that an output shaft be disconnected from an input shaft in case of failure of a driven mechanism so that driving of the driven mechanism can be halted and so the driving mechanism may not be damaged. In a typical arrangement, an input shaft is provided having a clutched end. An output shaft is provided adjacent the input shaft having a slidable clutched end. The slidable clutched end is under some external control in order to allow the slidable clutched end to retract, thereby disengaging the output shaft from the input shaft. Prior art devices have employed various methods of disconnecting such axially aligned and nonconcentric output shaft-input shaft arrangements. The present invention is the first, however, to be directed to providing a concentric shaft decoupling which replaces, with the fewest hardware modifications, a heat activated eutectic solder disconnect device. The present invention allows an IDG to be disconnected remotely, such as from an airplane cockpit whenever desired. Further, the present invention is the first specifically designed to operate within the narrow confines of an IDG.
Following is a discussion of some disconnect methods and the deficiencies thereof in a concentric shaft environment.
U.S. Pat. No. 4,086,991, which issued on May 2, 1978 to Swadley, and commonly assigned with the present invention, is directed to a thermally actuated disconnect coupling which includes a coupling shaft normally connected between a drive member and a driven member to transmit torque from the drive member to the driven member. Within the driven member, a fusible element such as an eutectic pellet supports the coupling shaft against axial movement during normal in-service use of the coupling. Providing the connection between the coupling shaft and the drive member are axially straight splines formed both on the coupling shaft and the drive member. At the other end of the coupling shaft, helical splines formed on the coupling shaft and the driven member provide means whereby torque is transmitted through the coupling shaft to the driven member. The axial length of the helical splines is greater than the axial length of the straight splines. When the pellet has melted, such as by overheating, an axially directed component transmitted by the helical splines propels the coupling shaft away from the drive member thereby disconnecting the drive and driven members. Swadley describes a thermal disconnect mechanism for an IDG which is not operable by an aircraft crew. As such, Swadley is useful when a purely thermal disconnect is sought. However, the present invention is directed to a different purpose: provision of a device remotely controllable which allows disconnect at a pilot's discretion and is therefore useful in a variety of malfunction conditions. Some of the malfunction conditions may not involve IDG overheating and therefore may not trigger the Swadley device.
U.S. Pat. No. 4,434,881, which issued on Mar. 6, 1984 to Denk et al., is directed to a disconnect member which is spline-connected to one end of a connecting drive shaft of an engine and a driven accessory, and is axially translatable into and out of coupling engagement with the engine. The disconnect member has a spiralled, axially ramped cam surface formed thereon which cooperates with a rotatable cam follower selectively movable into engagement therewith to axially drive the rotating disconnect member relative to the cam follower, thereby uncoupling the engine from its driven accessory. When the cam followers disengage from the cam surface, a reset spring automatically recouples the disconnect member to the engine. Denk et al. uses a rotating cam to withdraw a spline shaft from engagement. Denk et al. is not designed to retract a radially outward output shaft from a concentrically inward input shaft. Further, Denk et al. is not designed to replace an existing heat activated concentric shaft disconnect. Finally, Denk et al. is inappropriate for use within the tight confines of an IDG, where a shaft disconnect must be shaped to be appropriately received within the space allotted. The instant invention uses a stationary cam for the purpose of retracting a retaining pin and not for directly withdrawing the spline shaft.
U.S. Pat. No. 4,167,695, which issued on Sept. 11, 1979 to Phillips, is directed to a system intended primarily for use in multi-engined aircraft. A kit for each engine includes a generator drive train connected to an engine to be driven thereby, a driving formation for connection to a generator, and a coupling or clutch in the drive train to decouple a generator in case of mechanical or electrical failure. Signal means may be located in the cockpit in the pilot's field of view to indicate generator failure. A switch operable by the pilot in response to the failure signal acts to remotely cause decoupling of the generator. The switch also operates means to deactivate any other decoupling switch to prevent mistakenly decoupling a properly functioning generator. Cross-connection switch means are connected to all engines and generators and may be actuated to electrically connect an active generator to the engine having the decoupled generator. The coupling or clutch uses a retaining latch internal to the shaft which is disengaged by axial movement of driving plunger under solenoid actuation to allow separation of dogteeth. Apart from the use of dogteeth, Phillips differs, both in structure and operation from the instant invention and is inappropriate for use with concentric shafts and within the narrow confines of an IDG.
U.S. Pat. No. 4,232,772, which issued on Nov. 11, 1980 to Brissey et al., is directed to a disconnect arrangement for high-speed aircraft generators and includes a disconnectable rigid, torque transmitting spring loaded curvic gears coupled between the driving and driven shafts. A plurality of flexible supported sear members mounted on the driven shaft engage the movable member of the curvic gears. The sears have tapered faces which engage correspondingly tapered shoulders on the movable curvic gear member. The sears are latched to hold the curvic gear members in contact by the armature of an electromagnet. The armature normally rides over the top of the gears maintaining them in contact with the tapered shoulder of the curvic gear member. When the electromagnetic armature is actuated to disengage the driving and driven shafts, the armature moves axially. This removes a retaining force from the tapered sears, allowing them to flex outwardly. The natural separating force of the spring loaded curvic gear causes the sear to ride upwardly on the tapered surface of the curvic shoulder until the sears and the shoulder disengage. This allows the spring loaded gears to separate terminating transmission of torque from the driving to the driven shaft. Brissey et al, therefore, uses spring loaded sears held in place by an electromagnetically moved armature. The sears are held in place mechanically. In the instant invention, the pins are lightly held by springs and mainly held by centrifugal force. In Brissey et al, the sears are moved outward by spring force. In the instant invention, the pins are driven in against spring force by a cam. Brissey et al. is not appropriate to replace a heat activated eutectic shaft disconnect mechanism as found in an IDG.
U.S. Pat. No. 3,603,175 which issued on Sept. 7, 1971 to Horton, is directed to an actuator having a clutch control mechanism arranged to set the actuator in a position in which it is driven by a motor via a worm wheel or in a manually driven position. The clutch control mechanism includes a yoke which is manually moved by a lever to urge the clutch member into the manual drive position. The yoke is locked in this position by a latch which bears against a rod attached to the yoke. In this position, the latch also bears against the worm wheel and is rotated when the latter is motor driven. Rotation of the latch allows the rod to drop into a hole in the latch and the clutch member moves into engagement with the worm wheel. Rotation of the worm wheel therefore automatically changes the actuator from manual drive to motor drive. Horton, therefore, uses a cam to drive a yoke which drives a dog clutch in and out of engagement. In Horton, the cam is actuated by a hand lever. In the instant invention, however, the cam action is derived from rotation of the shaft which is being disconnected. In other words, the shaft in the instant invention provides the rotation which causes pin actuation by the cam.
U.S. Pat. No. 3,080,030, which issued on Mar. 5, 1963 to Troeger, is directed to a high-speed torque transmission means with an emergency disconnect coupling or device for connecting and uncoupling a powered drive shaft and a driven shaft in an aircraft. Troeger uses an axial movement of a wedge to lock a second wedge in place which thereby retains disconnect teeth in engagement. In Troeger, therefore, actuation means are driven axially. In the instant invention, however, actuation means are primarily rotational; in particular, cam action is rotational. Troeger is inappropriate for disconnect of concentric shafts in an IDG.
U.S. Pat. No. 2,855,768, which issued on Oct. 14, 1958 to Plano, is directed to a latched release positive clutch which can be used between a motor and a driven device such as a generator. Apparently, Plano uses a retaining pin to hold the clutch in engagement. Retracting the pin causes spring force disengagement. Plano does not address actuation of the pin. In the instant invention, it is critical due to (A) the narrow confines of an IDG, (B) the configuration of the replaced thermal disconnect and (C) the arrangement of an annular cam that the pin be actuated in the manner shown.
U.S. Pat. No. 3,298,249, which issued on Jan. 17, 1967 to Nott, is directed to an actuating mechanism for valves of the kind incorporating a drive mechanism by which the valve may be selectively operated either manually or by power means such as an electric motor. Nott uses axial movement of a cam to dislodge a retaining pin. In Nott, the cam movement is reversible by actuation of a hand wheel or by the axial motion of the driven gear. Disconnect actuation is axial in Nott. In the instant invention, disconnect actuation is rotary.
None of the aforementioned inventions was designed to overcome the problem presented when an output shaft concentric with an input shaft is to be decoupled. Furthermore, these inventions were never designed to fit within the narrow confines of an IDG, where space is at a premium. Finally, none of these inventions was designed to replace a simple eutectic solder pin without major modifications to the IDG. Applicant's invention is the first to address the problem of providing a shaft disconnect for concentric shafts and is the first to do so while working within the narrow confines of an IDG and while requiring minimal modifications to an existing eutectic solder disconnect design.